Animals were sharpening their senses long before the Cambrian explosion, ancient tracks reveal

Animals were sharpening their senses long before the Cambrian explosion, ancient tracks reveal Lisa Lock Scientific Editor Robert Egan Associate Editor Tracks left by some of the earliest complex animals are giving new insights into how they experienced the world. New research reveals how these creatures started to understand their surroundings, paving the way for animal life to spread across the planet. Today, many of us take our five senses for granted. But what was it like for life beginning to sense the world for the first time? While the bodies of these animals are rarely preserved, the tracks they left behind might hold the answers. A new study examining these trace fossils has shown how animals went from taking their first stumbling steps to having purposeful journeys as their sensory abilities evolved over a period of 20 million years. As the senses of these animals improved, they would have been increasingly able to find food, locate a mate or migrate over long distances. Dr. Zekun Wang, our scientist who led the research, says that this was a landmark moment in the evolution of life. "For the first time, animals had the ability to understand the world," he says. "They could use their developing senses to piece together different information and use that to accurately locate and plan their routes towards resources." "As the range of their senses increased, they were increasingly able to systematically exploit resources and move into new niches. In turn, the variation of the seafloor drove the need for even greater sensory abilities and evolution in other parts of their body, such as their appendages." "These advancements improved their capacity to cope with selective pressures and laid the foundations for the animal-dominated world we have today." The findings of the study were published in the Proceedings of the National Academy of Sciences. What do we know about life in the Ediacaran? Historically, most of the focus on the evolution of early animal life has been on a period known as the Cambrian Explosion. This key time in the history of life on Earth lasted from around 539 to 519 million years ago, and is when most of the major animal groups first appear in the fossil record. However, more recent research has demonstrated that this "explosion" didn't happen all in one go. There were millions of years of build up to the event, starting towards the end of the preceding Ediacaran Period. The Ediacaran, which occurred between 635 and 539 million years ago, saw life transition from unspecialized groups of cells into more complex forms. As these were soft-bodied, we don't know what most of these species looked like because they're rarely preserved. Zekun's research focuses on trying to find out more about these animals. While body fossils only exist of a few species, such as Kimberella and Dickinsonia, he instead looks at what the tracks of Ediacaran animals reveal about their lives. His previous studies have shown that between 550 and 540 million years ago new body shapes and ways of moving were evolving. Having originally moved similar to amoeba, later species moved more like horseshoe crabs, snails and worms. This new study takes this research one step further. By examining the tracks of an animal, Zekun and his colleague Tianyun Shi can infer how well developed its senses were. "If an animal has a limited ability to sense its environment, it only gets information discontinuously," Zekun explains. "This means that it only finds resources when they stumble across it by random chance. So, the tracks they leave are normally long and aimless. "But as the senses of animals develop, they can sense resources from further away. We can see this in the tracks, as their path suddenly changes course to head towards food, shelter or whatever it might be. It's also more common for these tracks to cross themselves as the animals keep heading to and from these resources." How did early senses evolve? To track how these patterns changed over time, Zekun and Tianyun examined 231 fossilized tracks from around the world. Before 546 million years ago, the tracks are largely random and aimless, suggesting species with poor senses. The researchers' models infer that these animals may have only been able to sense less than a centimeter around themselves. Six million years later, shortly before the Cambrian Explosion, the sensory landscape was transformed. While animals with limited senses still existed, others were making more direct paths towards concentrated microbial mats and other resources. It's estimated that these organisms could have sensed about 10 centimeters of the surrounding landscape. This dramatic increase in their sensory abilities might have happened as these species first evolved to sense light, perhaps even with very basic vision. By 526 million years ago, in the midst of the Cambrian Explosion, animals could now sense as much as 15 centimeters away. While this still isn't far, it was around 12 times their own body width—about the same as a person sensing 4 meters around themselves. Of course, resources aren't the only reason that an animal changes course. In the future, Zekun hopes to investigate what other behaviors these species used to guide their direction. "There are many other simple behaviors, such as following boundaries or avoiding danger, that can reflect the senses of these organisms," Zekun adds. "We'll need to expand our model to be able to see whether this can be detected from the trace fossils, but it could offer even deeper insights into the capabilities of these animals." Publication details Zekun Wang et al, Trace fossils constrain the perceptual ranges of the earliest motile animals, Proceedings of the National Academy of Sciences (2026). DOI: 10.1073/pnas.2609730123 Journal information: Proceedings of the National Academy of Sciences Provided by Natural History Museum This story is republished courtesy of Natural History Museum. Read the original story here.